SYMPTOMS: Powdery, black spore masses of Ustilago avena replace
kernels and chaff causing a disease problem referred to as loose smut of oats. The
smutted heads can be seen as soon as heads emerge from the boot. Spore masses disperse
and may not be evident at harvest.
DISEASE CYCLE: This fungus survives as spores and/or mycelium
in the floral bracts or on halls. Not until germination of the oat grain
does the pathogen proceed to infect the seedling. The fungus infects the
seedling by penetrating into the coleoptiles and growing inside the plant until
panicle formation begins. The fungus then begins replacing the kernel tissue with
masses of spores. The fungal spores are then spread by wind and rain onto the
flowering heads of healthy plants.
Use certified, pathogen-free seed since infected seed is the only source of inoculum.